Nucleophilicity of diatomic Lewis bases MA in hydrogen-bonded complexes MA⋯HX: influence of the group and row of M in the periodic table.

Nucleophilicities NMA of diatomic Lewis bases MA acting as hydrogen-bond acceptors in complexes MA⋯HX are reported. The molecules MA were chosen so that the atom M adjacent to the atoms A directly involved in the hydrogen bonds belongs to Groups 13, 14, 15, 16 and 17 of the periodic table. The effects of changing atom M from rows 1 to 4 within a given group were also investigated. The hydrogen-bond donors HX involved in the complexes were HF, HCl, HBr, HI, HCCH, and HCP. Nucleophilicities NMA were determined from dissociation energies De for the process MA⋯HX = MA + HX by using De = cNMA·EHX + d, where EHX are electrophilicities of the Lewis acids HX, and c and d are constants. The order of NMA values was found to be Row 4 > Row 3 ∼ Row 2 ≫ Row 1 in each of the Groups 13, 15, 15, 16 and 17. The effect of adding an H atom to MA to give linear triatomic molecules HMA were considered. The reduced nucleophilicities ИMA = NMA/σmin (σmin is the minimum value of the molecular electrostatic surface potential of MA) as a function of the group and row of atom M were also discussed for diatomic molecules MA.